Straighten all bone chains in an armature
One option to do that would be to use Auto IK, which is located in 3D Viewport > Toolshelf > Options tab (use T to toggle open/close the Toolshelf). When Auto IK is turned on, you can select last bone of the chain and pull it straight to any direction you want. 

Alternatively (necessary if your hair chains are directly connected to head), you could use IK Solvers. In Pose Mode, select the last bone of the chain, key Shift + I, select To New Empty, and in the Properties panel > Bone Constraints tab, set the chain length to the right amount of bones. Then, you can use the empty object created earlier to pull the chain straight.